Phenotypic and genetic architecture of juvenile morphometry in Chinook salmon

Juvenile morphology can affect fitness of salmonids in nature, but the genetic basis for morphometry in salmonids is poorly understood. We mated chinook salmon in a half-sib/full-sib breeding design to determine the genetic and environmental components of morphometric variation. We characterized body size and shape in 20 progeny from each of 95 full-sib families by digitizing 30 landmarks on lateral, dorsal, and ventral images of the body form, and estimated genetic and environmental components of variance for 12 truss elements constructed from the landmarks. We then conducted principal component analyses of the phenotypic, genetic, and environmental covariance matrices for these elements. Most (83%) of the phenotypic variation in morphometry was expressed along axes of allometry, shape change during smoltification, and a three-dimensional body shape contrast (head width versus lateral profile depth). All morphometric traits showed substantial additive genetic variation and were highly correlated genetically as well as phenotypically, Principal components of genetic variation in morphometry resembled the phenotypic principal components. The analyses also detected strong environmental effects on body shape and indicated two distinct morphometric types arising from maternal or environmental sources. The results provide evidence for genetic coordination of body size and shape, which would be expected if these characters are tightly coupled developmentally.